The invention mainly relates to catalysts suitable in hydrogenation reactions, such as hydrogenation of hydrocarbons, e.g. hydrocracking, and hydrogenation of carbon monoxide, e.g. Fischer-Tropsch. The invention further relates to the catalysts themselves and to the use of these catalysts. The invention further relates to a process for producing normally gaseous, normally liquid and optionally solid hydrocarbons from synthesis gas, generally provided from a hydrocarbonaceous feed, for example a Fischer-Tropsch process.
Many documents are known describing processes for the catalytic conversion of (gaseous) hydrocarbonaceous feedstocks, especially methane, natural gas and/or associated gas, into liquid products, especially methanol and liquid hydrocarbons, particularly paraffinic hydrocarbons. In this respect often reference is made to remote locations and/or off-shore locations, where direct use of the gas, e.g. through a pipeline or in the form of liquefied natural gas, is not always practical. This holds even more in the case of relatively small gas production rates and/or fields. Reinjection of gas will add to the costs of oil production, and may, in the case of associated gas, result in undesired effects on the crude oil production. Burning of associated gas has become an undesired option in view of depletion of hydrocarbon sources and air pollution.
The Fischer-Tropsch process can be used for the conversion of hydrocarbonaceous feed stocks into liquid and/or solid hydrocarbons. Generally the feed stock (e.g. natural gas, associates gas and/or coal-bed methane, peat, biomass, coal) is converted in a first step into a mixture of hydrogen and carbon monoxide (this mixture is often referred to as synthesis gas or syngas). The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds ranging from methane to high molecular weight modules comprising up to 200 carbon atoms, or, under particular circumstances, even more.
Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier based support material and one or more metals from Group VIII of the Periodic Table, especially from the cobalt and iron groups, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703.
One catalyst for Fischer-Tropsch reactions is cobalt in titania. In one method to prepare such a catalyst, cobalt hydroxide (CO(OH)2) can be used as a starting material. This material impregnated onto a carrier, and then calcined to reduce to cobalt oxide (CoO); the cobalt is further oxidised (Co3O4). A calcined Fischer-Tropsch catalyst or catalyst precursor can be placed in a Fischer-Tropsch reactor. In the reactor the catalyst or catalyst precursor can be reduced. For example, cobalt oxide can be reduced to cobalt.
A suitable Fischer-Tropsch catalyst can comprise a catalytically active metal and a carrier, the carrier being ‘fixed’ onto a substrate. In many fixed-bed or packed bed reactors, there are several thousand elongate substrates, on which the catalyst material is supported so as to maximise possible catalyst and reactant interaction. The carrier can be ‘fixed’ onto one or more substrates using a ceramic ‘glue’. The carrier layer is usually applied as a smooth layer. Normally the aim is to prepare a catalyst of which the carrier layer on the support remains smooth and uncracked, even during use in a reactor.
Due to the raised temperature in most hydrogenation reactors, e.g. hydrocracking reactors or hydrocarbon synthesis reactors (e.g. 200-350° C.), there is frequently tension caused by the expansion of the usually metallic substrate, and the expansion of the catalyst material, especially the catalyst carrier material which is often a ceramic material, and/or the ceramic ‘glue’.
The term “catalyst material” as used herein typically refers to an active phase material, or a precursor thereof, with an inert carrier, such as a refractory oxide, present typically as nano-sized particles. The active phase material or precursor thereof may be a catalytically active metal or precursor thereof.
The tension, based on the different rates of thermal expansion, (thermal expansion coefficients), leads to erosion and attrition of the catalyst carrier, which frequently then loses its adhesion to the substrate, separates, and falls away.
It is generally considered that a smooth layer provides the best indication of the prevention of any cracking of the layer prior to use.
Thus, cracking has hitherto been considered an undesirable action, as it leads to an uncontrolled variation in the catalyst material layer. There are created many very small remaining particles of catalyst material which have insufficient strength and so catalyst material is lost due to adhesion failure caused by differences in thermal expansion between the catalyst material layer and the substrate.
This detachment clearly creates several problems. Firstly, the need to filter out any loose catalyst material or catalyst carrier from compounds formed by the reactants. Secondly, the reduced amount of catalytic activity in the hydrocarbon reactor, and thirdly, a change in the conditions around the now-bare substrate. These aspects commonly lead to the need to repair of the catalysts and of substrates in a hydrocarbon reactor. This results in reactor downtime and so reduction in the hydrocarbon conversion.
It would be an advancement in the art to provide an improved method of supporting a hydrocarbon synthesis catalyst material.